The present invention relates to a method for determination of temperature values in an internal combustion engine. In particular, the present invention is intended for use in connection with motor vehicles, for derivation of temperature values to be used in controlling the vehicle engine. The present invention also relates to an apparatus for such a control of an internal combustion engine.
In connection with vehicles powered by an internal combustion engine, there is a general desire to reduce the vehicle fuel consumption as far as possible. This, in turn, is based upon environmental demands aimed at reducing the amount of detrimental discharges to the atmosphere, and upon demands regarding good fuel economy of the vehicle.
In today""s motor vehicles, the supply of air and fuel to the engine is normally controlled by means of a computer-based engine control unit. This control unit is in a known manner, arranged for detecting signals representing a number of different operating variables of the vehicle, e.g. engine speed, load, engine coolant temperature, vehicle speed, etc. From these signals, the amount of fuel to be supplied to the engine is continuously determined, and the supply is then made by means of an injection device.
With the intention of limiting the fuel consumption of a vehicle, the control unit may be arranged, in a known way, so as to ensure that, during operation, a stoichiometric air/fuel mixture (i.e. a mixture where xcex=1) is fed to the engine. This guideline value can, however, not be achieved for all points of operation, due to limitations regarding the maximum allowed thermal load on the components of the engine and the exhaust system. For example, the temperature of the engine cylinder head and exhaust system, and in any existing turbocharger unit, must be held within certain predetermined maximum limits. Should these limits be exceeded, there would be a risk of damaging the components.
The risk of a high thermal load on the engine system and its components is particularly marked at high loads and engine rotational speeds. For such operating situations the engine exhaust gas temperature must be limited, so as not to become so high that there will be a risk for damage to the engine and its associated components, as discussed above.
According to the prior art, this cooling effect is obtained by supplying a certain excess amount of fuel to the engine during the above-mentioned operating conditions, such as when the vehicle driver applies full throttle. This will entail the fuel mixture being controlled so as to deviate from the stoichiometric mixture. More precisely, this increase in fuel supply is controlled to reach a certain level, corresponding to the exhaust gas temperature remaining lower than a predetermined limit value. The magnitude of this limit value may be based on empirical criteria, which in turn would be determined by engine tests, and would indicate a limit above which there is a risk of damage to certain sensitive components in the engine and exhaust system.
A major drawback with this known procedure relates to the fact that it is not always necessary to supply the excess fuel as quickly as the change in engine load, as the engine and exhaust system temperatures in any case do not increase as quickly as the load changes. This may in turn be attributed to thermal inertia in the various parts of the engine system. This often entails supplying an excess amount of fuel to the engine at high loads and engine speeds, which is a drawback as it increases the vehicle fuel consumption.
Within the relevant technical area, a system for controlling the fuel supply to an internal combustion engine of a vehicle is previously known from U.S. Pat. No. 5,103,791. This system comprises means for detection of the engine load and the engine coolant temperature. Based on these values of load and temperature, a value of the temperature in the engine exhaust system is estimated. This temperature value is the basis for a correction of the amount of fuel fed to the engine. In this way, the exhaust system temperature can be limited, reducing the risk of damage.
Another system for controlling the fuel supply to an internal combustion engine is described in U.S. Pat. No. 5,158,063. This system comprises means for estimating the temperature of at least one component in the engine system as a function of the current engine operating conditions. The air/fuel mixture supplied to the engine may then be controlled as a function of this estimated component temperature.
A common feature of these two known systems is that they include relatively simple models for the engine system temperature, in particular providing a control that does not account for the thermal inertia of the respective temperature-sensitive component, e.g. during a sudden increase of the load.
Consequently, there is a need for being able to provide temperature values that can be used in a better fashion when cooling the engine system.
An object of the present invention is to provide an improved method for determination of temperature values that may be utilized for such control.
In accordance with the present invention, this and other objects have now been realized by the discovery of a method for determining the temperature of at least one component associated with an internal combustion engine in a vehicle, the at least one component having an inherent thermal inertia associated therewith, the method comprising detecting the value of at least one predetermined variable associated with the operating condition of the internal combustion engine, the at least one predetermined variable comprising the rotational speed or load of the internal combustion engine, and deriving the temperature of the at least one component based upon the value of the at least one predetermined variable derived from the inherent thermal inertia. In a preferred embodiment, the deriving of the temperature comprises dynamic modeling of the detected value of the at least one predetermined variable whereby a dynamically corrected value of the temperature is obtained. Preferably, the dynamic modeling of the detected value of the at least one predetermined variable comprises low pass filtration.
In accordance with one embodiment of the method of the present invention, the deriving of the temperature comprises utilizing tables based on a predetermined relationship between measurement of the temperature and the detected value of the at least one predetermined variable. Preferably, the method includes storing the tables in a control unit for the internal combustion engine.
In accordance with another embodiment of the method of the present invention, the at least one predetermined variable includes the injection time, the injection angle, the temperature of coolant in the internal combustion engine, the temperature of air flowing into the internal combustion engine, the rotational speed of the internal combustion engine, the rate of flow of air flowing into the internal combustion engine, and the speed of the vehicle.
In accordance with another embodiment of the method of the present invention, the method includes providing changes in the detected value of the at least one predetermined variable, and wherein deriving of the temperature of the at least one component is based upon the changes.
In accordance with another embodiment of the method of the present invention, the method includes controlling the thermal load of the internal combustion engine based upon the determined temperature. Preferably, the at least one predetermined variable comprises at least two predetermined variables, and the method includes controlling the thermal load on the internal combustion engine based on one of the at least two predetermined variables representing the largest reduction in the thermal load of the internal combustion engine.
In accordance with another embodiment of the method of the present invention, the internal combustion engine includes a cylinder head and a turbocharger, and the at least one component is selected from the group consisting of the material of the cylinder head and the turbocharger.
In accordance with the present invention, apparatus has also been discovered for determining the temperature of at least one component associated with an internal combustion engine in a vehicle, the at least one component having an inherent thermal inertia, the apparatus comprising at least one sensor for detecting the value of at least one predetermined variable associated with the operating conditions of the internal combustion engine, the at least one predetermined variable comprising the rotational speed or the load of the internal combustion engine, and a control unit for controlling the air/fuel mixture supplied to the internal combustion engine based upon the value of the at least one predetermined variable, the control unit deriving the temperature of the at least one component based upon the value of the at least one predetermined variable derived from the inherent thermal inertia.
The method according to the present invention is intended for use with control of an internal combustion engine in a vehicle, and includes detecting data regarding predetermined variables of the engine and vehicle operating conditions, deriving temperature values of the material in at least one component associated with the engine, as a function of those variables, whereby control of the thermal load of the engine can be performed dependent upon at least those temperature values. The present invention is characterized in that the temperature values are derived dependent upon the thermal inertia inherent in the component when changing the rotational speed and/or the load of the engine.
The temperature values derived in accordance with the present invention may be utilized for control of the engine so as to cool it in an optimum way during e.g. sudden increases in load and speed. This, in turn, will ensure that certain predetermined critical material temperature values are never exceeded. This cooling, i.e. limitation of the thermal load on the engine system, may be achieved by utilizing the derived temperature values for control of the air/fuel mixture supplied to the engine, whereby an additional amount of fuel is supplied as a function of the derived temperature values. In this manner particularly the enrichment of the air/fuel mixture can be delayed until its cooling effect is required. This leads to a lower fuel consumption of the engine compared to the art.
The derivation according to the present invention is active within a certain xe2x80x9ccritical areaxe2x80x9d of engine operation, which is characterized by high loads and high speeds. Within this xe2x80x9ccritical areaxe2x80x9d there is a risk that some engine component might experience a temperature exceeding a critical value, thereby risking damage to that component This xe2x80x9ccritical areaxe2x80x9d is defined in this description as that area where the engine is normally controlled with an air/fuel mixture deviating from the stoichiometric relationship.
The temperature values derived according to the present invention allow the internal combustion engine to be controlled so as to limit the thermal load on the engine system. This can be achieved by using the derived temperature values for control of the air/fuel mixture supplied to the engine, whereby an additional amount of fuel is supplied as a function of the derived temperature values. In this manner, particularly the enrichment of the air/fuel mixture can be delayed until its cooling effect is really required. As an alternative, the thermal load on the engine system may be limited by injecting water or a corresponding coolant directly into one or more of the engine cylinders. This will provide environmental and economical advantages. Furthermore, the thermal load on the engine system may be limited by control of a thermostat associated with the engine cooling system. According to a further alternative, which is particularly advantageous for engines provided with a turbocharger unit, the thermal load may be limited by controlling the charge pressure of the turbocharger. This may be accomplished by regulating a wastegate valve in the turbocharger unit.
The present invention thus provides for improved engine control compared to the known systems, allowing engine fuel consumption to be reduced, particularly for operating circumstances with high load and rotational speed. Notwithstanding this, the present invention ensures that no temperature-critical engine component will reach a temperature exceeding a critical limit value, at which damage might occur.
Preferably, the present invention is implemented as a complementing software function in a known engine control unit Existing vehicle components are to a high degree used in combination with auxiliary software functions, without having to introduce any additional hardware components.